1. Field of Invention
The present invention relates to a fabrication method for a metal via. More particularly, the present invention relates to a method of removing polymer residues after tungsten etch back.
2. Description of Related Art
In a multilevel metallization process, tungsten is a common material for manufacturing a metal plug due to its excellent conductivity and high conductivity. Tungsten has also been used to replace aluminum alloy for making the metal plug, since a tungsten layer formed by chemical vapor deposition (CVD) provides better step coverage than an aluminum alloy layer does.
FIG. 1 is a schematic diagram illustrating polymer residues that remain after a tungsten etching back is applied in the conventional fabrication method for a metal via.
Referring to FIG. 1, a first metal layer 100 that is formed on a metal oxide semiconductor (MOS) device (not shown) and a substrate (not shown) is provided. A dielectric layer 102 is formed and patterned to form an opening 102a, which exposes a part of the first metal layer 100. A conformal metal barrier layer 104 is then formed on the patterned dielectric layer 102 and covers the profile of the opening 102a, wherein the metal barrier layer 104 may include a TiN, layer. A blanket metal layer 106, preferably a tungsten layer, is formed on the metal barrier layer 104, wherein the method for forming the tungsten layer 106 includes chemical vapor deposition (CVD). A tungsten etch back is performed to remove a part of the tungsten layer 106 outside the opening 102a until the top surface of the tungsten layer 106 in the opening is level with the top surface of the metal barrier layer 104.
However, large polymer residues 108 are easily produced due to a reaction that occurs as a result of tungsten etch back and remain on the metal barrier layer 104. Following the method mentioned above, the polymer residues 108 that remain on the metal barrier layer 104 inevitably provide a large resistance which affects the reliability of the device. Thus, the overall yield from the metal via fabrication process is reduced. Conventionally, a brush cleaning is adopted to remove the polymer residues, but it is known by those skilled in art that the jet cleaning and brush cleaning cannot effectively remove such polymer residue defects. Other methods, such as chemical mechanical polishing (CMP), are performed to remove the polymer residues produced during tungsten etch back. However, there are problems associated with using CMP, including the possibility that the etching solvent involved in the tungsten CMP may attack the metal barrier layer 104 with respect to different etching selectivity when etching is performed for a long period of time. Since the process window in this case is too narrow to control, the polymer residues 108 may not be thoroughly removed if the etching time is reduced.
The invention provides a method for lowering particle count after tungsten etch back, which method is applicable to a multilevel metallization process. A first metal layer is provided, with a patterned dielectric layer formed thereon so as to form an opening that exposes a part of the first metal layer between the patterned dielectric layer. A conformal metal barrier layer is then formed on the patterned dielectric layer and covers the profile of the opening, followed by forming a blanket tungsten layer, which fills the opening and covers the metal barrier layer. A tungsten etch back process is performed to remove a part of the tungsten layer outside the opening until the top surface of the tungsten layer in the opening is level with the top surface of the metal barrier layer.
As embodied and broadly described herein, the invention provides a method for lowering particle count after tungsten etch back. The method includes a plasma ashing step which is performed to eliminate the polymer residues that remain on the metal barrier layer after tungsten etch back is performed. An additional tungsten etch back process is performed to remove a tungsten oxide film that is formed subsequently, since an O2 gas involved in the plasma ashing step can cause oxidation reaction with the tungsten layer.
According to the present invention, the polymer residues produced after tungsten etch back are removed by performing plasma ashing, instead of by tungsten CMP which would damage the metal barrier layer. As a result, no large resistance is produced to affect the reliability of the device. Furthermore, tungsten etch back is performed after the plasma ashing step to remove the tungsten oxide film which increases the resistance of the metal via. Therefore, the overall yield from the fabrication process for the metal via is increased.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.